Been a while since your last workout? Don't worry. Scientists have discovered how to jog your muscles' memory and get fit fast

Five weeks and five days after giving birth, and a full nine months since running a single step, WH's Lesley Rotchford, 34, laced up her sneaks and banged out five miles. Her muscles groaned a bit from the abrupt reentry, but with 20 years of distance running under their belt, they remembered just what to do.

It's a phenomenon aptly called muscle memory. Simply put, when you teach your body how to do something—ride a bike, surf, strike some yoga poses, run a few miles—it creates a physiological blueprint. So even if you take some time off, you'll get back to where you were faster than it took you to learn the exercise in the first place. "Muscle memory stems from your body's learning not just how to perform a task, but also how to break down muscle tissue and then repair and rebuild it," explains William Kraemer, Ph.D., a professor in the department of kinesiology at the University of Connecticut at Storrs. "That physiological knowledge lets you come back from injury, surgery, and even pregnancy faster, easier, and often better than before," he says.

Athletes have taken advantage of muscle memory for decades. Exercise scientists have been studying it just as long. But you don't need to be an Olympian or have a Ph.D. to know how to reap the rewards. Here's how you can tap your muscle memory and enjoy the lifelong body benefits.

How Your Muscles Remember

Not surprisingly, the process of forging muscle memory originates in the brain. When you learn something new, whether it's how to do a split squat or how to snowboard, your brain fires up all the right motor units (nerves that signal muscle fibers to kick in) to help you perform the movements.

Once your muscle fibers get the memo from your brain to move, they start sending messages back. "When you move, you activate sensors (called proprioceptors) in your muscles, tendons, and joints that constantly give feedback to your central nervous system about where your body is in space, so it knows what muscles to fire next," says Adam Knight, Ph.D., an assistant professor of biomechanics at Mississippi State University. It's a continuous feedback loop from your brain to your muscles and back. "Your brain creates pathways through your central nervous system, and movements become automatic," adds Wayne Westcott, Ph.D., fitness research director at Quincy College in Massachusetts. Those well-worn pathways essentially become your muscle memory.

The more regularly you use these pathways, the more your muscle memory solidifies, even if you slack off for a while. Ohio University researchers put a group of women on a two-days-a-week strength-training program for 20 weeks, then let them lounge around for eight months. When they called them back to the gym along with a group of women who'd never lifted before, they found that the previously trained women had retained most of their muscle fibers. When they started pumping iron again, they made gains more rapidly than the women who had no history of strength training.

The same principle applies to any exercise, says Lee Hong, Ph.D., an assistant professor of kinesiology and neuroscience at Indiana University at Bloomington. "If you lay off an activity for too long, you'll get rusty, but those patterns are locked in," says Hong. "That's why, even after 10 or 20 years, you can get back on a bike and ride."

Until recently, researchers believed that these ingrained neuromuscular patterns were the primary reason for the rebound-after-a-layoff effect. But Norwegian scientists recently discovered something else that may be a game changer in the way we understand how the body gets—and stays—fit. Turns out, exercise also triggers longterm, possibly permanent, changes in your cells. In a study of mice, researchers found that after just six days of simulated strength training, the mice generated new nuclei in their muscle cells. This is a big deal, since these nuclei contain the DNA blueprint necessary to make new muscle. And months after the mice stopped training, even though their muscles had shrunk, those newly formed nuclei were still hanging around, waiting to be reactivated by exercise, says study leader Kristian Gundersen, Ph.D., of the University of Oslo. "It's not unrealistic to suspect that human muscles respond as quickly and that those nuclei last for decades, or even a lifetime," he says.

The more exercise you do, the more memory you can bank and the easier it is to make deposits. "It's like a health savings account," says Hong. And as with any savings account, it's best to start early—like now. Gundersen's research found that the ability to make new muscle decreases as you age. "The earlier you start and the more you build, the better off you'll be later in life," says Hong.

Your Body Never Forgets

There's no getting around this: If you take a few months (or years!) off from exercise, you will huff and puff and feel achy as your body gets back into the swing of things. But if you establish a history of fitness, your pain will be a lot more manageable. Any sweat equity you invest forges a cardiovascular and strength blueprint that helps you make gains faster and be less prone to soreness and injury than someone who has never lifted anything heavier than a glass of merlot or has run only when chased.

And there's more good news: Muscle memory's impact extends beyond general fitness. The physical changes your body undergoes while building a fitness platform help speed up your metabolism, make you more resilient to stress, and bolster your immune system, says Kraemer. "All these adaptations become ingrained physiologically," he adds. Muscle memory not only helps you get more from every workout but also "spills into your everyday life, making you a better-functioning human being."